System, apparatus, and method for blade clearance tuning

ABSTRACT

When connecting two elements that are moveable with respect to one another, someamount of clearance, i.e., spacing between the elements, is included to minimize friction between the elements. The present invention is directed to setting the clearance within a desired range, regardless of manufacturing tolerances of the two elements. In particular, the present invention is directed to power cutting tools wherein it is necessary to set the clearance between one or more reciprocating blades and a blade support member.

This is a division of application Ser. No. 09/475,069, filed Dec. 30,1999, now U.S. Pat. No. 6,415,515.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally directed to setting the spacingbetween two elements that are moveable with respect to one another. Thisspacing is commonly referred to as the “clearance” between the elements.Some amount of clearance, i.e., within a desired range, is included tominimize friction between the elements. However, manufacturingtolerances and conventional assembly techniques can result in deviationsoutside the desired range of clearance.

In particular, the present invention is directed to power cutting toolswherein it is necessary to set the clearance between one or more moving,e.g., reciprocating, blades and a blade support member. The term “powercutting tool” includes hand-held power tools such as a hedge trimmers,as well as mechanisms which are not hand-held but whose operation iscontrolled by the hands of a user, e.g., a lawn mower.

2. Description of the Related Art

In order to perform a desired task using a cutting tool, it is importantthat the relatively moving blade or blades be separated from each otheror from a relatively stationary blade by an optimum clearance foraccomplishing the task efficiently.

Conventionally, blade clearance for cutting tools is preset by themanufacturer. Alternatively, it is known to use a spring mechanism toforce relative contact between the blades. It is also known to use jamnuts to periodically adjust the clearance. However, manynon-professional users do not know how or take the time to make thenecessary adjustments.

Examples of known cutting devices associated with reciprocating bladesinclude U.S. Pat. No. 5,771,583 to Kremsler et al. U.S. Pat. No.5,689,887 to Heywood et al., U.S. Pat. No. 5,075,972 to Huang, U.S. Pat.No. 4,879,303 and 4,868,988 to Han, U.S. Pat. No. 4,075,760 to Germain,U.S. Pat. No. 3,579,827 to Grahn, U.S. Pat. No. 3,200,493 to Dodegge,and U.S. Pat. No. 2,275,180 to Holsclaw.

SUMMARY OF THE INVENTION

An object of the present invention is to set, within a desired range,the clearance between first and second elements that are constrained toa prescribed relative motion. Thus, it is a further object of thepresent invention to constrain the first and second elements to theprescribed relative motion while maintaining friction in a desiredrange. It is yet a further object of the present invention to set anoptimal range for the clearance between the first and second elements.

An advantage of the present invention is that the need for grindingblades to give tighter control of their thickness is eliminated.

The above objects and advantages, as well as other objects andadvantages that will become clear from the following description of thepresent invention, are realized by a system for setting a clearancebetween relatively movable elements. The system comprises a firstelement; a second element relatively movable with respect to the firstelement; and a third element penetrating the second element along anaxis, the third element being fixed against axial displacement withrespect to the first element. The third element having a first axialportion extending a first dimension along the axis between first andsecond axial ends, the first dimension exceeding a thickness of thesecond element along the axis, and a second axial portion beingconnected to the first axial portion at the second axial end and havingan enlarged radial dimension relative to the first portion, the secondelement being interposed between the first element and the secondportion. Whereby the first axial end extends into a depression in thefirst element a second dimension that is less than the differencebetween the first dimension and the thickness.

The above objects and advantages, as well as other objects andadvantages that will become clear from the following description of thepresent invention, are also realized by a system for setting bladeclearance in a power cutting tool. The system comprises a blade supportmember; a first cutting blade relatively movable with respect to theblade support member; a second cutting blade relatively moveable withrespect to the blade support member and with respect to the firstcutting blade; and a spacer penetrating the first and second cuttingblades along an axis, the spacer being fixed against axial displacementwith respect to the blade support member. The spacer having a firstaxial portion extending a first dimension along the axis between firstand second axial ends, the first dimension exceeding a combinedthickness of the first and second cutting blades along the axis, and asecond axial portion being connected to the first axial portion at thesecond axial end and having an enlarged radial dimension relative to thefirst portion, the first and second cutting blades being interposedbetween the blade support member and the second portion. Whereby thefirst axial end extends into a depression in the blade support member asecond dimension that is less than the difference between the firstdimension and the combined thickness.

The above objects and advantages, as well as other objects andadvantages that will become clear from the following description of thepresent invention, are also realized by an apparatus for setting aclearance between relatively movable elements connected by a spacerhaving a flange. The apparatus comprises a first jaw adapted forengaging a first one of the relatively movable elements; a second jawincluding a surface adapted for engaging a second one of the relativelymovable elements, the surface having a recess adapted for engaging theflange; and a press moving the first and second jaws toward one another.Wherein the second jaw is adapted for displacing the spacer to deformthe first one of the relatively moveable elements, and the surface isadapted for stopping spacer displacement by engaging the second one ofthe relatively movable elements.

The above objects and advantages, as well as other objects andadvantages that will become clear from the following description of thepresent invention, are also realized by a method of setting a clearancebetween relatively movable elements. The method comprises orientingadjacent first and second relatively movable elements against a firstpress jaw; inserting a third element along an axis extending through anaperture in the second element, the third element including a firstaxial portion extending a first dimension along the axis between firstand second axial ends, the first dimension exceeding a thickness of thesecond element along the axis, and a second axial portion beingconnected to the first axial portion at the second axial end and havingan enlarged radial dimension relative to the first portion, the secondelement being interposed between the first element and the secondportion; aligning a second press jaw against the third element and inopposition to the first press jaw; pressing the third element along theaxis against the first element; deforming the first element with thefirst axial end so as to create a depression extending into the firstelement a second dimension; whereby axial clearance between the firstelement, the second element, and the second portion is equal to thefirst dimension less a combined total of the thickness and the seconddimension.

These and other objects and advantages of the present invention are setforth in the description that follows, and in part will be readilyapparent to those skilled in the art from the description and drawings,or can be learned by practice of the invention. These objects andadvantages of the invention can be realized and obtained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred embodiments according tothe present invention refer to the accompanying drawings, whereinidentical numerals indicate like parts.

FIG. 1 schematically illustrates a first preferred embodiment of thepresent invention.

FIG. 2 is a cross-section view taken along line II—II on FIG. 1.

FIG. 3 schematically illustrates a second preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIGS. 1 and 2, a blade 10 is relatively movablewith respect to a blade support member 20 supporting the blade 10. Aspacer 30 constrains the relative movement of the blade 10 with respectto the blade support member 20 to a prescribed path. A fastener 40 cansecure the spacer 30 to the blade support member 20.

According to a preferred embodiment of the present invention, the blade10 includes an aperture 12 that extends through the blade 10 from afirst surface 10A to a second surface 10B. The shape of the aperture 12at its intersection with the surfaces 10A or 10B can be a circle, apolygon, or any other shape. According to a most preferred embodiment,the aperture 12 includes an elongated slot having a pair ofsubstantially parallel major sides 12A and 12B. The locus of midpointsbetween the sides 12A,12B define a path 14 that can be linear,curvilinear, or a combination of linear and curvilinear segments.

According to a preferred embodiment of the present invention, the blade10 is supported for reciprocal movement with respect to the bladesupport member 20. The blade support member 20 includes a face 22generally confronting the surface 10A. In the present disclosure, theexpression “support member” refers to any three dimensional elementincluding, but not limited to a sheet of material having a generallyplanar, convex, or concave topography, a partial or complete enclosure,or a solid body.

According to a preferred embodiment of the present invention, the spacer30 penetrates the blade 10 by extending through the aperture 12.According to a most preferred embodiment, the spacer 30 includes a firstportion 32 and a second portion 34. The first portion 32 has a first end32A contiguously contacting the face 22 and a second end 32B connectedto the second portion 34. A cross-sectional dimension of the firstportion 32, e.g., the diameter of a circle, generally corresponds to thedistance between the sides 12A, 12B. Thus, relative movement of theblade 10 with respect to the blade support member 20 is constrained tomovement along the path 14 without significant lateral deviation towardeither of the sides 12A, 12B. The second portion 34 has a largercross-sectional dimension than that of the first portion 32. Thus, theblade 10 is sandwiched between the second portion 34 and the bladesupport member 20. According to a most preferred embodiment of thepresent invention, the first and second portions 32,34 are configured ascoaxial right circular cylinders, with the second portion 34 having alarger diameter than the first portion 32.

According to a preferred embodiment of the present invention, the lengthof the first portion 32, i.e., from the first end 32 A to the second end32B, is greater than the thickness of the blade 10, i.e., from the firstsurface 10A to the second surface 10B. According to a most preferredembodiment of the present invention, the first end 32A is received in adepression 22A in the face 22. Referring to FIG. 1, the length of thefirst portion 32 is L1, the depth of the depression 22A is D, thethickness of the blade 10 is T, the clearance between the surface 10Aand the face 22 is C1, and the clearance between the surface 10B and thesecond portion 34 is C2. Thus, the sum of the clearances between theblade 10, the face 22, and the second portion 34 is set to be thedifference between the thickness of the blade 10 and the length of thefirst portion 32 less the depth of the depression 22A relative to theface 22. This relationship is expressed in Equation (1).

(C 1 +C 2)=(L 1 −D)−T  (1)

Thus, according to the present invention, the sum of the clearances(C1+C2) is not affected by deviations in the blade thickness T or thefirst portion length L1 inasmuch as the depression depth D is adjustedto account for these deviations.

The sum of the clearances (C1+C2) is set by a preferred apparatus 50according to the present invention. The apparatus 50 includes a firstjaw 52 and a second jaw 54 that are driven toward one another in apressing operation. The first jaw 52 engages the blade support member 20and provides a reaction force against the force used to form thedepression 22A. The first jaw 52 can include a recess 52A for definingthe boundary of the depression 22A or for freely accommodating a firstterminus 40A of the fastener 40. The second jaw 54 includes a face 56having a recess 56A that engages a pressing end 34A of the secondportion 34 for pressing the spacer 30 against the face 22 in order toform the depression 22A. The recess 56A can also freely accommodate asecond terminus 40B of the fastener 40. The first terminus can includethreads which threadably engage a nut.

According to a preferred embodiment of the present invention, the depthof the recess 56A relative to the face 56 is greater than the length ofthe second portion 34, i.e., from the pressing end 34A to a shoulder end34B at the connection to the second end 32B of the first portion 32.Referring to FIG. 1, the depth of the recess 56A is R, and the length ofthe second portion 34 is L2. Thus, the sum of the clearances between theblade 10, the face 22, and the second portion 34 is set to be thedifference between the length of the second portion 34 and the depth ofthe recess 56A. This relationship is expressed in Equation (2).

(C 1 +C 2)=R−L 2  (2)

Thus, variations within the desired range for the sum of the clearances(C1+C2) depend solely on the manufacturing tolerances of the recessdepth R and the second portion length L2, which are more easilycontrolled than the manufacturing tolerance of the blade thickness T.

The desired range of values for the sum of the clearances (C1+C2) can bemore precisely controlled according to a preferred method of the presentinvention. Initially, the spacer 30 is extended through the aperture 12and the blade 10 is arranged adjacent to the blade support member 20.Thus, the first end 32A of the spacer 30 confronts the undeformed face22 of the blade support member 20. The first jaw 52 is brought intoengagement with the blade support member 20 to provide a reaction forceopposing the force forming the depression 22A, which is applied by thesecond jaw 56 against the pressing end 34A of the spacer 30. The firstand second jaws 52,54 are pressed toward one another such that thespacer 30 deforms the blade support member 20, i.e., forms thedepression 22A. The depression 22A is completely formed when the face 56of the jaw 54 engages the surface 10B of the blade 10. Finally, thefirst and second jaws 52,54 are withdrawn from one another. The sum theclearances (C1+C2) is established within a desired range that isindependent of variations in blade thickness T or first portion lengthL1.

Of course, numerous variations can be practiced within the scope of thepresent invention. Rather than facilitating a relative reciprocatingmotion between the blade 10 and the blade support member 20, the presentinvention can facilitate relative rotating or pivoting motion betweenthe blade 10 and the blade support member 20. The spacer 30 can be fixedto the blade 10 and pass through an aperture in the blade support member20. The first portion 32 or the second portion 34 of the spacer 30 canhave any cross-sectional shape, i.e., they need not be circular. Thedepression 22A can be formed by a hot pressing operation, e.g., heatingthe spacer 30 so as to melt and/or soften a portion of the blade supportmember 20. Such a hot pressing operation can be performed in place of orin addition to the cold pressing operation described above. Rather thanhaving the aperture 12 penetrating an interior portion of the blade 10,the spacer 30 can cooperatively engage an edge of the blade 10.

Additional blades can be supported by a single spacer 30 for relativemotion with respect to the blade 10 and to the blade support member 20.Because the amount of blade clearance according to the present inventionis not affected by variations in blade thickness, a common spacer 30 canconnect any number of relatively moving blades and a blade supportmember.

Specifically, FIG. 3 illustrates a first blade 10 and a second blade IIthat are each relatively translatable with respect to the blade supportmember 20. The second blade 11 is sandwiched between first blade 10 andthe blade support member 20 such that a first surface 11A of the secondblade 11 generally confronts the face 22 of the blade support member 20,and a second surface 11B of the second blade 11 generally confronts thefirst surface 10A of the first blade 10.

The spacer 30 penetrates the second blade 11 in substantially the samemanner as the first blade 10. The length L1 of the first portion 32 ofthe spacer 30 is greater than the combined thicknesses of the first andsecond blades 10,11, i.e., the sum of the distances from the surface 10Ato surface 10B and from the surface 11A to the surface 11B. Referring toFIG. 3, the length of the first portion 32 is L1, the depth of thedepression 22A is D, the thickness of the first blade 10 is T1, thethickness of the second blade 11 is T2, the clearance between the face22 and the surface 11A is C1, the clearance between the second portion34 of the spacer 30 and surface 10B is C2, and the clearance between thesurfaces 10A and 11B is C3. Thus, the sum of the clearances between theface 22, the second blade 10, the first blade 11, and the second portionis set to be the difference between the combined thicknesses of thefirst and second blades 10,11 and the length of the of the first portion32 less the depth of depression 22A. This relationship is expressed inEquation (3).

(C 1 +C 2 +C 3)=(L 1 −D)−(T 1 +T 2)   (3)

Thus, according to the present invention, the sum of the clearances(C1+C2+C3) is not affected by deviations in the blade thickness (T1 +T2)or the first portion length L1 inasmuch as the depression depth D isadjusted to account for these deviations.

The identical reference numbers are used to indicate features in FIG. 3that are the same as in FIG. 1. A duplicate description of thesefeatures is omitted with regard to this second embodiment. Moreover, theembodiment shown in FIG. 3 can be practiced in accordance with the sameapparatus 50 and the same method of fabrication described with referenceto FIG. 1.

According to the preferred embodiments, apparatuses, and methods of thepresent invention, it is possible to provide a more precisely controlledamount of blade clearance. For example, the manufacturing tolerance fora blade is approximately ±0.0025 inches and the manufacturing tolerancefor a spacer is approximately ±0.004 inches. Thus, for a conventionaltwo-blade cutting tool, the variation of the clearance is ±0.009 inches.In contrast, the manufacturing tolerance for the recess 56A according tothe present invention is approximately ±0.001 inches; however, theeffect of the manufacturing tolerance for the blades is eliminated.Thus, for the two-blade cutting tool shown in FIG. 3, the variation ofthe clearance is ±0.005 inches. This reduction in the variation of theclearance greatly improves cut quality.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative devices, shownand described herein. Accordingly, various modifications can be madewithout departing from the spirit and scope of the general inventiveconcept as defined by the appended claims and their equivalents.

We claim:
 1. An apparatus for setting a clearance between relativelymovable elements connected by a spacer having a flange, the apparatuscomprising: a first jaw adapted for engaging a first one of therelatively movable elements; a second jaw including a surface adaptedfor engaging a second one of the relatively movable elements, saidsurface having a recess of sufficient depth so as to engage the flangeto deform the first one of the relatively movable elements and limitspacer displacement by engaging said surface with the second one of therelatively movable elements; and a press moving said first and secondjaws toward one another.
 2. The apparatus according to claim 1, whereinsaid recess extends from said surface into said second jaw a distanceadapted to be greater than a thickness of the flange.
 3. The apparatusaccording to claim 1, wherein said first jaw includes a recess adaptedto accommodate deformation of the first one of the relatively movableelements caused by the spacer.
 4. The apparatus according to claim 1,wherein said second jaw further including a heater adapted for heatingthe spacer and softening and/or melting the first one of the relativelymovable elements.
 5. A method of setting a clearance between relativelymovable elements, the method comprising: orienting adjacent first andsecond relatively movable elements against a first press jaw; insertinga third element along an axis extending through an aperture in saidsecond element, said third element including: a first axial portionextending a first dimension along said axis between first and secondaxial ends, said first dimension exceeding a thickness of said secondelement along said axis, and a second axial portion being connected tosaid first axial portion at said second axial end and having an enlargedradial dimension relative to said first portion, said second elementbeing interposed between said first element and said second portion;aligning a second press jaw against said third element and in oppositionto said first press jaw; pressing said third element along said axisagainst said first element; deforming said first element with said firstaxial end so as to create a depression extending into said first elementa second dimension; and engaging a surface of said second press jaw withsaid second element so as to stop displacement of said third element,said surface including a recess adapted for engaging said second axialportion of said third element; whereby axial clearance between saidfirst element, said second element, and said second portion is equal tosaid first dimension less a combined total of said thickness and saidsecond dimension.
 6. The method according to claim 5, wherein saidsecond press jaw includes a recess having a depth equal to a sum of saidaxial clearance and an axial dimension of said second axial portion. 7.The method according to claim 5, further comprising: orienting a fourthrelatively movable element adjacent to said second element; whereby saidthird element is inserted through said second and fourth elements alongsaid axis.